This invention relates to a method for continuously producing a pulp from agricultural fibers to be used ultimately in the papermaking industry. The invention also relates to a manufacturing system for accomplishing this purpose.
Paper is formed from fibers derived primarily from wood, and can also be made from cotton, straw, flax, and other vegetable fibers. The paper is formed from matted or felted fibrous sheets formed on a fine wire screen from a liquid suspension pulp. The isolation and preparation of fibers in an acceptable form for papermaking generally involves the processes of pulping, bleaching, and refining.
The pulping process depends for its success upon the differences in the chemical and physical properties between the fibers themselves and the regions responsible for fiber bonding. The pulping process involves the separation of the fibrous elements from each other by means of mechanical or chemical action.
The raw fibers produced during pulping are often given a bleaching or brightening treatment to remove or convert colored material to a colorless form. The exact nature of the chemical reactions which occur during bleaching are not too well understood because of the complex nature of the bleaching agents, and the chromophores, that is, the chemical groups which give rise to color in molecules.
Bleaching reactions are also complicated by the fact that large volumes of water are necessary, and which become contaminated. The recovery and conversion of the water is difficult and expensive. Therefore, reuse of the water for other purposes in papermaking is discouraged. Considerable research has been devoted to high consistency bleaching to minimize water usage, and the use of less polluting chemicals.
The last step before papermaking involves "beating and refining," often called stock preparation. The purpose of this step is to produce a greater degree of bonding and strength in the finished sheet. Chemicals and other additive materials are often added in this stage of the process, and the pulp then becomes ready for conversion into paper.
Declining stocks of wood have substantially increased the cost of papermaking in recent years. Moreover, the large amounts of water used in the pulping process which become polluted have led to efforts to minimize water usage, or to recycle it for other purposes.